Polymeric materials such as plastics are highly valuable for their strength and ability to be readily molded, extruded, or otherwise formed into a variety of shapes. However, if a plastic object is deformed or bent during or after molding, stress (or stored energy) can be introduced into the object. Such stored energy can cause undesirable deformation (e.g., warping) of the object and can result in movement or creep of the polymeric material as a result of the stress. Cracking, crazing or weakening of the object can result. In addition, the chemical or solvent resistance of a polymeric article may be adversely affected by stresses.
Although such stress or stored energy can dissipate over time (a process known as stress relaxation), it is often preferable to move quickly dissipate the stored energy. Previously-reported methods for relaxing stresses include annealing of the object in an oil bath, heating the object in a conventional oven, or exposing the object to infra-red or microwave radiation (e.g., using infra-red lamps or microwave sources). These processes generally involve the annealing of the entire object and can be rather slow and somewhat cumbersome. Moreover, such methods can cause shrinkage or other undesirable changes in the properties of the polymeric article.
Improved methods for reducing stresses in polymeric materials are therefore needed.